Armored fiber optic assemblies

ABSTRACT

Armored fiber optic assemblies and methods are disclosed that include a dielectric armor and at least one bend-resistant multimode optical fiber. The dielectric armor has an armor profile, thereby resembling conventional metal armored cable to the craft. The dielectric armor provides additional crush and impact resistance and the like for the optical fibers and/or fiber optic assembly therein. The dielectric armor is advantageous to the craft since it provides the desired mechanical performance without requiring the time and expense of grounding like conventional metal armored cables. Additionally, the armored fiber optic assemblies can have any suitable flame and/or smoke rating for meeting the requirements of the intended space. The use of at least one bend-resistant multimode optical fiber allows for improved bend performance for the armored fiber optic assemblies, allowing for tighter cable routing as compared to armored fiber optic assemblies having conventional multimode optical fiber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior application Ser. No.12/888,865, filed Sep. 23, 2010, which claims the benefit of U.S.Application No. 61/247,459, filed on Sep. 30, 2009, the entire contentsof both of which are hereby incorporated by reference herein.

This application is related to U.S. application Ser. No. 12/261,645,filed on Oct. 30, 2008, now U.S. Pat. No. 7,702,203, U.S. ApplicationNo. 61/168,605, filed Apr. 9, 2009, and U.S. application Ser. No.12/748,925, filed Jul. 2, 2010, which are incorporated herein byreference.

BACKGROUND

1. Field of the Disclosure

The present disclosure relates generally to optical fiber assemblies,and in particular relates to armored fiber optic assemblies having adielectric armor and desirable crush performance and attenuationproperties.

2. Technical Background

Conventional fiber optic cables include optical fibers that conductlight for transmitting voice, video and/or data. The construction offiber optic cables should preserve optical performance when deployed inthe intended environment while also meeting the other additionalrequirements for the environment. For instance, indoor cables for riserand/or plenum spaces may require certain flame-retardant ratings to meetthe demands of the space. In other words, these flame-retardant ratingsare in addition to mechanical requirements or desired characteristicsfor the space. Mechanical requirements or characteristics such as crushperformance, permissible bend radii, temperature performance, or thelike are preferred to inhibit undesirable optical attenuation orimpaired performance during installation and/or operation within thespace. In addition to the mentioned requirements, riser and/or plenumspaces may require a ruggedized design for meeting the demands of thespace.

By way of example, some indoor applications use a fiber optic cabledisposed within an armor layer for providing improved crush performancein riser and/or plenum spaces. For instance, conventional armoredconstructions have a fiber optic cable disposed within a metallicinterlocking armor for creating a robust construction. Specifically, onetype of well-known metallic interlocking armor is a “BX armor” or a“Type AC” cable. This metal armor is spiral wound about the fiber opticcable so that the edges of the adjacent wraps of armor mechanicallyinterlock, thereby forming a robust armor layer that also acts as abend-limiting feature for the assembly. However, there are disadvantagesfor this conventional interlocking armor construction. For instance,fiber optic cables having a metallic armor require additional hardwareand/or installation procedures for grounding the metallic armor to meetsafety standards, thereby making installation time-consuming andexpensive.

FIG. 1 shows several prior art examples of interlocking armored cables10 having a metallic armor layer 12 (typically aluminum) that serves toprotect and preserve optical performance of cables 14 therein. Sincemetallic armor layer 12 is conductive, it must be grounded to complywith the National Electrical Code (NFPA 120) safety standard. This addsto the complexity and expense of installing a metal-armored fiber opticcable. Additionally, the metallic armor can be plastically deformed(i.e., permanently deformed), which can pinch the cable and causeelevated levels of optical attenuation. Nevertheless, the market andcraft prefer the design and handling of this rugged cabling.

Manufacturers have attempted to design dielectric armor cables toovercome the drawbacks of the conventional metallic armor constructions,but to date a commercial solution is lacking. For instance, U.S. Pat.No. 7,064,276 discloses a dielectric armor cable having two syntheticresin layers where the hard resin layer has continuous spiral groove cutcompletely through the hard resin layer along the length of the armor.The hard resin layer is intended for bend control by having adjoiningedge portions of the spiral groove abut at the desired minimum bendradius. However, one skilled in the art would recognize this design doesnot provide the craft with all of the desired features. Moreover, it canbe difficult for the craft to recognize the cable of the '276 patent asan armored cable layered because it has a smooth outer surface, whereasconventional metal armored cables are easily identified by the craft asdepicted by FIG. 1.

Furthermore, with the increase in the deployment of optical networkssuch as data centers, a need has arisen for increasing the performance,manageability, handleability and flexibility of armored fiber opticcables. Unlike long-haul applications, data centers and the liketypically use a multimode optical fiber instead of single-mode opticalfiber. Because the space in a data center is rather limited, armoredcables often need to be deployed in tight spaces and with relativelytight bends. If the particular armored cable is not capable of suchtight bends because of the attenuation concerns with respect to themultimode fiber it carries, it is much more difficult to deploy thecable.

Therefore, there is a need in the art for armored fiber optic cableswith superior mechanical properties, including the ability to bendwithout being constrained by the bending limits of conventionalmultimode optical fibers.

SUMMARY

The disclosure is directed to armored fiber optic assemblies having adielectric armor and at least one optical fiber. The dielectric armorcan have an armor profile, thereby resembling conventional metal armoredcable to the craft. The dielectric armor provides additional crush andimpact resistance to the optical fibers and/or fiber optic assemblytherein.

The dielectric armor is also advantageous to the craft since it providesthe desired mechanical performance without requiring the time andexpense of grounding like conventional metal armored cables.Additionally, armored fiber optic assemblies can have any suitable flameand/or smoke rating for meeting the requirements of the intended space;however, the assemblies may have outdoor applications or indoor/outdoorapplications.

The use of optical fiber, such as bend-resistant optical fiber, allowsfor improved bend performance at low delta attenuation for the armoredfiber optic assemblies, allowing for tighter cable routing as comparedto armored fiber optic assemblies having conventional multimode opticalfibers.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments of the invention,and are intended to provide an overview or framework for understandingthe nature and character of the invention as it is claimed. Theaccompanying drawings are included to provide further understanding ofthe invention, and are incorporated into and constitute a part of thisspecification. The drawings illustrate the various example embodimentsof the invention and, together with the description, serve to explainthe principles and operations of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of three different prior art interlockingarmor cables and illustrates the characteristic helical shape of themetal interlocking armor layer;

FIG. 2A is a side cut-away view of a first example embodiment of anarmored fiber optic assembly having a dielectric armor according to thepresent invention;

FIG. 2B is a side cut-away view of a second example embodiment of anarmored fiber optic assembly having a dielectric armor according to thepresent invention;

FIG. 3A is a cross-section of the armored fiber optic assembly of FIG.2A taken along the line 3A-3A;

FIG. 3B is a cross-section of the armored fiber optic assembly of FIG.2B taken along the line 3B-3B;

FIG. 3C is a cross-section similar to FIGS. 3A and 3B, but genericallydepicts a fiber optic assembly disposed within a dielectric armor inorder to show a radius Rc of the fiber optic assembly and an innerradius R_(I) of the dielectric armor;

FIG. 4 is a schematic diagram of an example embodiment of an armoredfiber optic assembly formed in a bend radius (i.e., a loop);

FIG. 5A is an enlarged perspective view and FIG. 5B is a close-up viewof the armored fiber optic assembly of FIG. 2A showing a partiallongitudinal cross-section of the dielectric armor superimposed on agrid for reference of the shapes of the layers;

FIG. 6A is an enlarged view of a portion of the dielectric armor of FIG.5B further showing various dimensions associated therewith;

FIG. 6B is an enlarged perspective view of a portion of a genericarmored profile showing the geometry of used for finite-element modelingof the dielectric armor;

FIG. 7 is a plot of the true stress (Pa) vs. the true strain (%) for twodifferent representative rigid materials and a representative non-rigidmaterial that are suitable for use as a portion of the dielectric armor;

FIG. 8A is a table of design parameters determined by finite-elementmodeling at two different minimum strain levels for the non-rigidmaterial shown in the true stress vs. true strain graph of FIG. 7;

FIGS. 8B through 8E respectively set forth tables of design parametersdetermined by finite-element modeling at different minimum strain levelsfor two different rigid materials shown in the true stress vs. truestrain graph of FIG. 7;

FIGS. 9A and 9B are plots of the data in FIG. 8A depicting thedielectric armor band thickness (T1) vs. the groove-length to pitchratio (2L2/P) for the non-rigid material with the two different minimumstrain levels on the same plot;

FIGS. 9C and 9D are plots of the data in FIGS. 8B and 8C depicting thedielectric armor band thickness (T1) vs. the groove-length to pitchratio (2L2/P) for the first rigid material for two different strainlevels on respective plots;

FIGS. 9E and 9F are plots of the data in FIGS. 8D and 8E depicting thedielectric armor band thickness (T1) vs. the groove-length to pitchratio (2L2/P) for the second rigid material for two different strainlevels on respective plots;

FIG. 10A is a perspective view of another embodiment of an armored fiberoptic assembly having an inner and outer layer;

FIG. 10B is a perspective view of yet another embodiment of an armoredfiber optic assembly;

FIG. 10C is a perspective view of the inner layer of the dielectricarmor of FIG. 10B of still another embodiment of an armored fiber opticassembly;

FIG. 10D is a perspective view of still another embodiment of an armoredfiber optic assembly;

FIG. 11 is a schematic diagram of an explanatory extrusion system formaking dielectric armor;

FIG. 12 is a schematic cross-sectional view of the crosshead of theextrusion system of FIG. 11;

FIG. 13 is a schematic side view illustrating another method of formingthe dielectric armor;

FIG. 14 is a partial, cross-sectional view of another explanatoryexample of a crosshead wherein the profiling feature is within thecrosshead die;

FIG. 15 is a side view of an example extrusion system wherein theprofiling feature is located external to the crosshead and impresses theprofile into the dielectric armor;

FIG. 16 is a perspective view of an example roller-type deforming memberthat is used to impress the armor profile into the dielectric armor;

FIG. 17 is a front view illustrating the use of two roller-typedeforming members to impress the armor profile into the dielectricarmor;

FIG. 18 is a side view of an example bend-resistant multimode opticalfiber (“BR-MM fiber”) used in example embodiments of the armored fiberoptic assembly of the present invention;

FIG. 19 is a schematic representation (not to scale) of across-sectional view of the multimode fiber of FIG. 18;

FIG. 20 shows an example schematic representation (not to scale) of therefractive index profile of the cross-section shown in FIG. 19, whereinthe depressed-index annular portion is offset from the core by an innerannular portion and is surrounded by an outer annular portion; and

FIG. 21 is a plot of the change in attenuation (“Δ attenuation”) in dBversus bend radius in mm for a standard 50 micron multimode fiber and a50 micron BR-MM fiber at wavelengths of 850 nm and 1,300 nm.

DETAILED DESCRIPTION

Reference is now made in detail to the present preferred embodiments ofthe invention, examples of which are illustrated in the accompanyingdrawings. Whenever possible, identical or similar reference numerals areused throughout the drawings to refer to identical or similar parts. Itshould be understood that the embodiments disclosed herein are merelyexamples with each one incorporating certain benefits of the presentinvention. Various modifications and alterations may be made to thefollowing examples within the scope of the present invention, andaspects of the different examples may be mixed in different ways toachieve yet further examples. Accordingly, the true scope of theinvention is to be understood from the entirety of the presentdisclosure in view of, but not limited to the embodiments describedherein.

FIGS. 2A and 2B depict side cut-away views of two different armoredfiber optic assemblies 20 having a fiber optic assembly 30 including atleast one optical fiber 40 disposed within a dielectric armor 70. In anexample embodiment, the at least one optical fiber 40 is abend-resistant multimode fiber (BR-MM fiber). Details of an exemplaryBR-MM fiber are discussed in greater detail below.

Dielectric armor 70 is non-conductive and has an outer surface (notnumbered) that includes an armor profile (not numbered) and in thisembodiment is generally formed in a spiral manner along a longitudinalaxis. As used herein, “armor profile” means that the outer surface hasan undulating surface along its length that looks similar to theconventional metal armor (i.e., a undulating shape along the length ofthe armor). Dielectric armor 70 includes one or more layers such as aninner layer 72 and an outer layer 74, but other constructions arepossible. For instance, dielectric armor 70 may consist of a singlelayer such as inner layer 72. Preferably, inner layer 72 is a rigidmaterial and outer layer 74 is a non-rigid material; however, it ispossible to use a non-rigid material for inner layer 72 and have therigid material as outer layer 74. As used herein, “rigid material” meansthe material has a Shore D hardness of about 65 or greater and“non-rigid material” means the material has a Shore D hardness of about60 or less. The dielectric armor 70 is advantageous since it providescrush resistance, meets the desired flame or smoke rating, and/or otherdesirable characteristics, but does not require grounding likeconventional metal armor. For instance, armored fiber optic cables canhave a diametral deflection of 3.3 millimeters or less during a crushresistance test as discussed below.

FIG. 2A depicts a dielectric armor 70 having multiple layers with thearmor profile formed essentially in the inner layer 72 (i.e., the rigidlayer) and the outer layer 74 (i.e., the non-rigid material) having anessentially uniform thickness over inner layer 72. Another embodiment ofdielectric armor 70 is constructed by eliminating outer layer 74. Asshown, a fiber optic assembly 30 is housed within dielectric armor 70.In this embodiment, fiber optic assembly 30 is a fiber optic cable thatincludes a cable jacket. However, fiber optic assemblies of otherembodiments can have other constructions and/or structures such asassemblies that eliminate the cable jacket. By way of example, the fiberoptic assembly may be a stranded tube cable, monotube cable, micromodulecable, slotted core cable, loose fibers, tube assemblies, or the like.Additionally, the fiber optic assemblies can include any suitablecomponents such as water-blocking or water-swelling components,flame-retardant components such as tapes, coatings, or other suitablecomponents. Specifically, fiber optic assembly 30 of FIG. 2A includes acentral strength member having a plurality of tight-buffered opticalfibers stranded thereabout and a cable jacket. Any fiber opticassemblies 30 may have any suitable fiber count such as a 6-fiber MICcable or 24-fiber MIC cable available from Corning Cable Systems ofHickory, N.C.

FIG. 2B depicts another multi-layer dielectric armor 70 with the armorprofile essentially in the outer layer 74 (i.e., the non-rigid material)with inner layer 72 (i.e., the rigid material) having an essentiallyuniform thickness under outer layer 74. Fiber optic assembly 30 of FIG.2B includes a plurality of ribbons 56 disposed in a tube 32, therebyforming an assembly. In both embodiments of FIG. 2A and FIG. 2B, innerlayer 72 has a “continuous annular cross-section.” As used herein,“continuous annular cross-section” means there are not spiral grooves,opening, or slits that cut entirely thru the layer. Additionally, outerlayer 74 of the embodiments of FIG. 2A and FIG. 2B are formed from anon-rigid material. Using a non-rigid material as the outer layer isadvantageous for several reasons such as providing impact protection forthe assembly and/or allowing the selection of a material having alow-smoke characteristic or flame-retardant property.

One skilled in the art will appreciate the extreme difficulty in meetingthe desired mechanical characteristics, low-smoke characteristics,and/or flame-retardant characteristics and the like with the armoredfiber optic assemblies of the present invention. This difficulty isespecially true for the NFPA262 plenum rating. Simply stated, thepolymer mass of the armored fiber optic assemblies provides a relativelylarge combustible mass, thereby making it difficult to meet bothmechanical requirements and flame/smoke requirements. Advantageously,certain embodiments of the armored fiber optic assemblies meet both themechanical and the flame/smoke requirements such as riser-ratings and/orplenum-ratings. Of course, assemblies disclose herein can have outdooror indoor/outdoor applications.

FIGS. 3A and 3B respectively depict cross-sectional views of armoredfiber optic assemblies 20 of FIGS. 2A and 2B taken respectively alongthe lines 3A-3A and 3B-3B. For the purposes of simplicity inillustration, the dielectric armor 70 is depicted with a uniformcross-section that does not reflect the spiral of the armor profile. Asshown, armored assemblies 20 may include a free space 90 disposedbetween an outer surface of fiber optic assembly 30 and a dielectricarmor inner surface. FIG. 3C shows a generic illustration of an armoredfiber optic assembly 20 having an outer radius R_(C) and dielectricarmor 70 having an inner radius R_(I). The amount of free space 90 ischaracterized by a separation ΔR between outer surface of fiber opticassembly 30 and the inner surface of dielectric armor 70, whereinΔR=R_(I)−R_(C). Including free space 90 in the construction aids inpreserving optical performance during crush events and the like asdiscussed below. By way of example, free space 90 is typically about 2millimeters or less, but free space values larger than 2 millimeters arepossible.

If intended for indoor use, embodiments preferably are flame-retardantand have the desired flame-retardant rating depending on the intendedspace such as plenum-rated, riser-rated, general-purpose, low-smokezero-halogen (LSZH), or the like. For instance, suitable materials forthe layers of dielectric armor 70 may be selected from one or more ofthe following materials to meet the desired rating: polyvinyl chloride(PVC), polyvinylidene fluoride (PVDF), flame-retardant polyethylene(FRPE), chlorinated polyvinyl chloride (CPVC), polytetra flourethylene(PTFE), polyether-ether keytone (PEEK), Fiber Reinforced Polymer (FRP),low-smoke zero-halogen (LSZH), polybutylene terephthalate (PBT),polycarbonate (PC), polyethylene (PE), polypropylene (PP), polyethyleneterephthalate (PETE), and aerylonitaile butadiene styrene (ABS). Theskilled artisan understands that many factors of the design can affectflame-ratings and finding a suitable designs and/or materials to meet agiven rating can be extremely challenging. One example of an armoredfiber optic assembly similar to FIG. 2A having a riser rating includesinner layer 72 formed from a PVC available from Teknor Apex under thetradename 8015 and outer layer 74 is formed from a plenum-grade PVCjacket material available from AlphaGary under the tradename 1070L.Additionally, this PVC/PVC combination results not only in the desiredflame-retardant rating, but also meets the desired mechanicalrobustness. Of course, other suitable material combinations are alsopossible.

Besides flame- or smoke-ratings, mechanical characteristics of interestinclude minimum bend radius, impact resistance, crush-resistance,durability of the dielectric armor, susceptibly to plastic deformation,etc. Material characteristics such as the hardness, modulus, etc. alongwith geometry can influence the desired characteristics/opticalperformance for the armored fiber optic assemblies. For instance, theinner layer and/or the outer layer should have a suitable modulus ofelasticity. By way of example, a modulus of elasticity at 1% strain forthe rigid material is about 1200 MPa or greater and the modulus ofelasticity at 1% strain for the non-rigid material is between about 300MPa and about 1200 MPa. Of course, these are merely explanatory examplesand other values for the modulus of elasticity are possible with theconcepts disclosed herein.

One mechanical property provided by the dielectric armor is itsresistance to being crushed (i.e., crush resistance). One test thatquantifies crush resistance applies a load of 300 Newtons/centimeterover a 10 centimeter length of the armored fiber optic assembly (i.e.,3000 N total load) for a period of ten minutes at which time adiameteral deflection is measured under load. An optical-performancebased crush test is given by the ICEA596 crush standard, which applies aload of 300 Newtons/centimeter for ten minutes and then measures deltaattenuation of the optical fibers under load. The ICEA596 crush standardrequires a maximum delta attenuation of less than 0.60 dB for multimode(MM) optical fibers at a reference wavelength of 1300 nm and a maximumdelta attenuation of 0.40 dB or less for single-mode (SM) optical fibersat a reference wavelength of 1550 nm. Armored fiber optic assemblies 20were tested according to the ICEA596 crush standard as well as otherperformance tests as discussed herein. Additionally, assembliesdisclosed herein can meet other standards such as GR409 or the like.

Specifically, mechanical testing was conducted on MM optical fiberversions of armored fiber optic assemblies similar to FIG. 2A having24-fiber MIC cables for fiber optic assembly 30 and other embodimentshaving a 6-fiber MIC cables. MM versions were tested since they are moresensitive to optical attenuation and a better indicator of opticalperformance than SM versions. The testing of the MM versions was alsoconducted at two different reference wavelengths. Additionally, thedielectric armor 70 for the two different structures (24-fiber and6-fiber) had different geometries as discussed below and shown in detailin FIG. 5B. For instance, the armor profile for the 24-fiber MIC cableembodiments had an average pitch of 10±1 millimeters, an average webthickness of 1±0.2 millimeters, and an average band thickness of 1.6±0.2millimeters for the inner layer. The armor profile for the 6-fiber MICcable embodiments had an average pitch of 10±1 millimeters, an averageweb thickness of 0.8±0.2 millimeters, and an average band thickness of1.3±0.2 millimeters for the inner layer.

The dielectric armor provided exceptional crush performance.Specifically, Table A lists the results for the two different versionsunder the ICEA596 crush standard along with similar testing underelevated crush loads of 3500 Newtons and 4000 Newtons. Table A lists thedelta optical attenuation results for each crush load with the resultsat 1300 nanometers listed first and the result at 850 nanometers second.

TABLE A Crush Performance Testing 3000 Newtons 3500 Newtons 4000 NewtonsFiber Optic (1300 nm/ (1300 nm/ (1300 nm/ Assembly 850 nm) 850 nm) 850nm) Assembly with 6- 0.14 dB/0.12 dB 0.09 dB/0.08 dB 0.24 dB/ Fiber MICCable 0.16 dB Assembly with 0.06 dB/0.05 dB 0.05 dB/0.05 dB — 24-FiberMIC Cable

As shown, the crush performance results for the tested armored fiberoptic assemblies were much lower than the under the ICEA596 crushstandard. The results for both the MM fiber counts were about 0.20 dB orless at 1300 nm and 3000 Newtons, which is one-third of the pass valuefor the ICEA596 crush standard, which is 0.60 dB or less. Moreover, theload was increased to 4000 Newtons and the results still were less thanhalf of the pass value at 3000 Newtons. Additionally, the values for SMarmored fiber optic assemblies were not tested but should have deltaattenuation of about 0.20 dB or less at 1300 nm and 3000 Newtons sincethey are less sensitive than MM optical fibers.

Another mechanical property of the armored fiber optic assemblies istheir flexibility (e.g., the ability to bend without damage and/orcausing elevated levels of attenuation). Generally speaking, the maximumamount of bending that armored assemblies can withstand without kinking,cracking, separating and/or causing elevated optical attenuation ischaracterized by its minimum bend radius. FIG. 4 shows a loop 94 ofarmored fiber optic assembly 20 formed into a bend radius R_(B). Inother words, the bend radius R_(B) is the distance from the center tothe inner surface of the assembly when formed into a coil as shown byFIG. 4. The bend radius R_(B) may be related to other dimensions and/orcharacteristics of the armored fiber optic assembly. For instance, theminimum bend radius R_(B) may be related to the maximum outer diameterof armored fiber optic assembly (e.g., 2 times the maximum armored fiberoptic assembly radius R_(T)). By way of example, if armored fiber opticassembly 20 has an outer diameter of 2R_(T) then minimum bend radiusR_(B) may be a multiple of the outer diameter of 2R_(T) such asR_(B)(min)≧10R_(T). Of course, the assembly can have a minimum bendradius that is smaller than provided by the relationship. In an exampleembodiment where at least one optical fiber 40 is a BR-MM fiber, theminimum bend radius will be smaller than where optical fiber 40 is aconventional MM fiber.

Table B lists the delta optical attenuation results for two differentbend radii, specifically, at 10R_(T) and 8R_(T) for the armored fiberoptic assemblies described above.

TABLE B Bend Radii Testing Fiber Optic 10R_(T) Bend Radius 8R_(T) BendRadius Assembly (1300 nm/850 nm) (1300 nm/850 nm) Assembly with 6- 0.01dB/0.01 dB 0.02 dB/0.01 dB Fiber MIC Cable Assembly with 24- 0.04dB/0.05 dB — Fiber MIC Cable

As shown, the delta optical attenuation performance for the bend radiustesting was relatively low for the assembly with the 6-fiber MIC cableand for the assembly with the 24-fiber MIC cable at a bend radius of20R_(T). Data for the smaller bend radius of 16R_(T) is not given sincethe values at 20R_(T) were somewhat elevated. Thus, the testedassemblies performed extremely well in the bend radii testing whencompared with the ICEA596 standard. Other variations or embodiment canhave much higher levels of optical attenuation such as 0.60 dB or lessduring bending so long as the performance is acceptable.

Table C lists the delta optical attenuation results for impact testingfor the armored fiber optic assemblies described above. Impact testingwas conducted using two different masses, specifically, 2 kg and 6 kg atreference wavelengths of 1300 nm and 850 nm. Impact testing included twoimpacts at three separate locations (e.g., about 150 millimeters apart)for each assembly and the maximum delta attenuation for impacts of eachassembly is listed in Table C.

TABLE C Impact Testing Fiber Optic 2 kg 6 kg Assembly (1300 nm/850 nm)(1300 nm/850 nm) Assembly with 6- 0.00 dB/0.00 dB 0.00 dB/0.01 dB FiberMIC Cable Assembly with 24- 0.00 dB/0.00 dB 0.00 dB/0.01 dB Fiber MICCableAs shown, the delta optical attenuation performance for the impacttesting showed little to no delta optical attenuation for eitherassembly at either mass. Overall, the tested armored fiber opticassemblies proved comparable with, or better, than conventional metallicarmor cable assemblies.

FIG. 5A is an enlarged perspective view and FIG. 5B is a close-up viewof the armored fiber optic assembly of FIG. 2A showing a partiallongitudinal cross-section of the dielectric armor superimposed on agrid G for referencing the shapes of the layers. Armored profile has apitch P (i.e., a generally repeating shape that forms the armoredprofile in a spiral manner along the longitudinal axis) that includes aweb 102 and a band 110. The geometry of the armored profile is discussedbelow in more detail with respect to finite-element modeling performed.As best shown in FIG. 5B, the armored profile of this embodiment isgenerally formed with inner layer 72 having a curvilinear profile formedin a spiral along the longitudinal axis and outer layer 74 has agenerally uniform thickness formed over the curvilinear profile of innerlayer 72. Two factors that influence the mechanical performance of thedielectric armor are geometry of the armored profile and the materialcharacteristics of the layers.

FIG. 6A depicts an enlarged cross-sectional view of a portion of thedielectric armor of FIG. 5B superimposed on grid G with certaindimensions of the armor profile shown. As shown, the dielectric armorincludes web 102 and band 110. Inner layer 72 of band 110 has athickness T1 and the web 102 of inner layer 72 has a thickness T2 asshown. As shown on grid G, web thickness T2 is defined asT2=T1−d_(O)−d_(i), where an outer groove depth d_(O) is the heightdifference between the band and the web of inner layer 72, and an innergroove depth d_(i) is the height difference between the band and the webof inner layer 72. Moreover, a total groove depth d_(O)+d_(i) is the sumof the outer groove depth d_(O) and inner groove depth d_(i). In thisillustration, outer layer 74 has a thickness T3 that is essentiallyuniform along the length of the armor profile, but the either or both ofthe layers could have the armor profile. Dielectric armor 70 has aninner radius R₁ and an outer radius that is R₁+T₁.

FIG. 6B is an enlarged perspective view of a portion of the layer of thedielectric armor having the armor profile showing genericgeometry/dimensions used for finite-element modeling of the same. FIG.6B depicts an armor profile that is shaped very closely to a stepprofile, which provides excellent mechanical characteristics when theproper geometry is selected. However, in practice it is difficult tomanufacture the armor profile nearly as a step profile at relativelyhigh line speeds as shown in FIG. 6B. Consequently, manufactureddielectric armor with the armored profile has a profile that is shapedin a rounded, sloped or the like fashion as generally depicted in FIG.6A.

Finite-element analysis was conducted on the model of FIG. 6B tosimulate the shape of manufactured profiles like shown in FIG. 6A. Usingfinite-element analysis, the inventors discovered certain dimensionand/or relationships that provide desired mechanical characteristics forthe armored profile. FIG. 6B depicts one-half pitch P/2 for the armoredprofile (i.e., the one-half pitch P/2 only depicts a fraction of the web102 and a fraction of band 110. The one-half pitch P/2 of the armorprofile has a length given by the sum of length L1 (i.e., the fractionalportion of the band), length L_(T) (i.e., a transitional portion betweenthe band and web), and length L2 (i.e., the fractional portion of theweb). Additionally, for the purpose of simplicity only the layer withthe armor profile of the dielectric armor was modeled since itcontributes to the majority of the mechanical characteristics for thedielectric armor. Consequently, the web has a length referred to as agroove length 2(L2) herein, which is two times the length L2.

FIG. 7 is a graph having three different curves of true stress (Pa) vs.true strain (%) representing two different generic dielectric materials.Specifically, as labeled the first and second curves represent differentrigid materials and the third curve represents a non-rigid material asdefined herein, and may be employed in dielectric armor 70.Specifically, the first rigid material is a PVC available from TeknorApex under the tradename SRP 2009, the second rigid material is also aPVC available from Teknor Apex under the 8015 family name, and thenon-rigid material is a flame-retardant PVC available from AlphaGaryunder the tradename AG2052. Examples of rigid materials are rigidthermoplastics (such as rigid PVC, CPVC, glass/fiber reinforcedplastics, etc.), while examples of non-rigid materials are flexiblethermoplastics (such as polyolefins, PVC, PVDF, FRPE, etc.). As shown,after the knee in the curve of the rigid materials a negative slope ornear zero (i.e., small) positive slope occurs in a respective region RG1or RG2. On the other hand, the curve for the non-rigid material does nothave a negative slope or a near zero slope like the rigid materials.

Dielectric materials that exhibit a region with a negative slope or anear zero positive slope in the stress-strain curve at or below thelimiting design strain such as at the region RG1 of the first rigidmaterial in FIG. 7, require special attention to inhibit bending strainsfrom locally concentrating in the web of the armor profile. Simplystated, if the first rigid material operates in region RG1 of FIG. 7(e.g., the 5% to 25% strain zone, which is material specific) itlocalizes the strain at one location of the web during bending, whichmay cause the web 102 to undesirably separate from band 110. Thus,region RG1 of strain with a negative slope or a near zero positive slopeshould be avoided. On the other hand, outside region RG1 (i.e., a strainlevel that significantly exceeds 25%) the strain is more evenlydistributed along the web, thereby inhibiting band/web separation duringbending. In other words, the failure strain for the rigid materialshould be beyond the region RG1 (i.e., the failure strain level for thismaterial should exceed 25%), thereby inhibiting undesirable band/webseparation for the intended application. Whereas the failure strainlevel for materials without the region RG1 such as the non-rigidmaterial depicted in FIG. 7 may allow for a wider range of failurestrain levels.

Likewise, the region RG2 for the second rigid material should be avoidedfor the same reasons as discussed above. However, the second rigidmaterial has a relatively low positive slope beyond region RG2 so thatsignificantly exceeding the region RG2 means that a much higher strainlevel is required to inhibit band/web separation. Consequently,different rigid materials may require different minimum strain levelsfor inhibiting web-band separation. By way of example, a minimum strainlevel of about 80% is necessary for the second rigid material to inhibitweb-band separation.

Moreover, it was determined that the total groove length 2(L2) should begreater for rigid materials that exhibit a region with a near zeropositive slope or a negative slope in the stress-strain curve at or nearthe failure strain as indicated by region RG1 or RG2 to inhibitseparation of the web from the band of the armor profile. Consequently,material characteristics along with band/web geometry for the materialcharacteristics should be selected for providing the desired performance(e.g., crush, bending, optical performance, etc) for the armored fiberoptic assemblies.

Additionally, the modulus of elasticity at 1% strain for the materialsof FIG. 7 was determined from the true stress-true strain curves. Themodulus of elasticity for the non-rigid material (AG2052) was about 320MPa. Whereas, the modulus of elasticity for the first rigid material(SRP 2009) was about 1537 MPa and the modulus for the second rigidmaterial (8015) was about 3088 MPa, which is about twice the value ofthe first rigid material.

FIG. 8A depicts Table 1 which has exemplary dimensions in millimetersfor the design window of a first modeled material (i.e., the non-rigidmaterial AG2052). Specifically, Table 1 lists exemplary dimensions forT1, T2, groove length, groove depth, and groove pitch for minimum designstrains of 40% and 80% with the armor carrying 100% of the load. Inother words, the loading for the modeling was performed with thedielectric armor carrying 100% of the applied 3000 Newton crush loadwith a deflection of 3 millimeters or less in order to provide anacceptable performance for the design window. However, the fiber opticassembly within the dielectric armor may carry some of the crush loaddepending on several factors such as amount of free space, type of fiberoptic assembly, and the like. Simply stated, all of the modelingrepresented in FIGS. 8A-8F model the extreme case where the dielectricarmor would carry 100% of the crush load and bending load. Consequently,some armored fiber optic cable designs may have acceptable performance,but not fall within the design window of the curves shown in FIGS. 9A-9Fbecause the fiber optic assembly was carrying a fraction of the crushload. Simply stated, some assemblies may have the dielectric armorcarrying a portion of the load along with the fiber optic assemblycarrying a portion of the load, thereby providing a larger designwindow. Likewise, during bending the fiber optic assembly within thedielectric armor may contribute to the bending performance, but this wasnot considered in the finite element modeling. Illustratively,dielectric designs with relatively longer groove lengths and relativelylarger total groove depths may not perform well in modeling that carries100% of the load, but when constructed with a suitable fiber opticassembly can have acceptable performance due to the fiber optic assemblycarrying a fraction of the load. Some parameters that affect loadsharing between the fiber optic assembly and the dielectric armorinclude free space, construction of the fiber optic assembly such asjacket thickness, and the like.

The minimum design strain is the minimum percent true strain at whichfailure occurs (i.e., the ultimate strain), which is the case for all ofthe modeling. For instance, the first column of data of Table 1 listsarmor profile dimensions that have strain of 80% strain or more whilemeeting the desired bend and crush criteria. The desired bend criteriapermits a bending radius R_(B) of 5 diameters of the fiber opticassembly (i.e., 10 radii of the fiber optic assembly) with no band/webseparation and the crush criteria has an optical attenuation of 0.6 dBor less. Likewise, the next four columns of data in Table 1 representrespective sets of armor profile dimensions that result in failure witha strain of 40% or greater while meeting the same bending and crushperformance. In a similar fashion, the remaining columns of Table 1 listother sets of armor profile dimensions that result in failure at theindicated strain levels. Additionally, all of the different dielectricarmor modeled in Table 1 had the same inner radius R_(I) slightly below6 millimeters.

Using the data from Table 1 (FIG. 8A), families of curves for the bandthickness versus a dimensional ratio for the armor profile of anexemplary non-rigid material were determined and plotted in FIGS. 9A and9B. Specifically, FIGS. 9A and 9B illustrate six curves for the bandthickness T1 vs. a ratio (i.e., (2L2)/P) of groove length to pitch forthe two different minimum strain limits (i.e., strain of 40% or more andstrain of 80% or more) and the three different total groove depths(do+di). As shown, families of curves are plotted based upon the totalgroove depths (do+di) of 0.5 millimeters, 0.75 millimeters, and 1.0millimeters for the two different strain levels, which are depicted onthe same graph to illustrate the changes in the design window.Alternatively, the total groove depth is calculated by T1−T2, which isequivalent to (do+di) as shown in FIG. 6B. Further, FIG. 9B is anenlarged view of the lower left-hand corner of the plot of FIG. 9A,thereby showing the detail of the extended design window for the curvesdirected to the 80% minimum design strain.

The respective areas bounded by the different curves representrespective design windows for the given total groove depth at the givenstrain level. For instance, the area bounded by the bold solid linecurve represents the total groove depth of 1.0 millimeter at a strain of40% or more. Designs outside the area bounded by the 1.0 millimeter/40%minimum strain curve may have issues with elevated levels of strain,and/or failure (band/web separation) during bending and the like. Forinstance, a design with a 3.1 millimeter band thickness and groovelength/pitch ratio of 0.5 at a groove depth of 1.0 millimeter and 40%minimum strain falls outside of this bounded area and may have issueswith passing crush performance. On the other hand, these dimensions havesuitable crush performance when the groove depth is 0.75 millimeters and40% minimum strain since it is bounded by that 0.75 groove depth curveas shown by FIG. 9A. Simply stated, for the given loading and designparameters for the respective curve: (a) points below the curve did notmeet the desired crush performance; (b) points to the left of the curvedid not meet the desired bending performance; and (c) points to theright of the curve did not meet the desired aesthetic appearance (i.e.,the groove was too long relative to the pitch). By way of example,suitable aesthetic appearance has the groove length between about 20percent and about 80 percent of the pitch.

The enlarged view shown in FIG. 9B, depicts that the design windows forthe 80% minimum strain curves are larger than the counterpart designwindows (i.e., the same total groove depths) for the 40% minimum straindesign windows. For instance, the 80% minimum strain windows extendfarther to the left as shown in the lower left corner of FIG. 9B. Thus,as shown by plotting of the modeling of Table 1 in FIGS. 9A and 9B,certain ratios and/or dimension relationships along with the materialcharacteristics provide the armor profile with the desired performanceduring bending and the like.

FIGS. 8B and 8C respectively depict Tables 2 and 3 with exemplarydimensions in millimeters for the design window of a first modeled rigidmaterial, namely, SRP 2009. Like Table 1, Table 2 lists exemplarydimensions for T1, T2, groove length, groove depth, and groove pitch forminimum strains of 40% and Table 3 lists data for minimum strains of80%. Like before, the modeled data from Tables 2 and 3 was used forcreating graphs of the modeled design window with the dielectric armorcarrying 100% of the load.

Specifically, FIGS. 9C and 9D are similar to FIG. 9A since theygraphically show the curves plotting the band thickness T1 vs. a ratio(i.e., (2L2)/P) of groove length 2L2 to pitch P for the given totalgroove depths (d_(O)+d_(i)) at a given minimum strain level.Specifically, the graph of FIG. 9C illustrates the design space with astrain of 40% or more and the graph of FIG. 9D depicts the design spacewith a strain of 80% or more. As shown, FIGS. 9C and 9D show that thedifference in the design space between the two different strain levelsis more pronounced with the first rigid material (FIGS. 9C and 9D)compared with the non-rigid material (FIGS. 9A and 9B). For instance,the designs windows at 40% minimum strain are more sensitive to changesin the total groove depth (d_(O)+d_(i)). This pronounced difference isdue to the negative slope of the stress vs. the strain curve as shown inFIG. 7 in the proximity of the 40% strain limit for the high-strengthmaterial. Consequently, greater groove-length to pitch ratios andthicknesses (T1) are required for meeting bending requirements (e.g.,without band/web separation, etc.) when designing with materials thatexhibit small positive slopes or negatives slopes (i.e., a trough in thestress strain curve) in the proximity of the failure strain.

If a material has such a trough in the stress vs. strain curve (i.e., asmall positive or negative slope in the stress vs. strain curve like asshown in FIG. 7) while the failure strain is significantly greater thanthe strain level at the trough, then smaller groove/pitch ratios andthicknesses T1 can be employed. Strains initially concentrate in web 102of dielectric armor 70 as it is bent. If sufficient strain hardening isnot available before the failure strain is reached (i.e., if the troughregion of the stress vs. strain curve is too close to the failurestrain), then web 102 of thickness T2 will fail and separate.

FIGS. 8D and 8E respectively depict Tables 4 and 5 with exemplarydimensions in millimeters for the design window of a second modeledrigid material, namely, a material from the 8015 family. Tables 4 and 5list exemplary dimensions for T1, T2, groove length, groove depth, andgroove pitch for respective minimum strains of 80% and 110%. Higherminimum strains were required for the second rigid material because theregion RG2 is larger and the true stress-true strain curve has ashallower slope than the first rigid material. Like above, the modeleddata from Tables 4 and 5 is used for creating graphs of the modeleddesign window. The loading for the modeling of the second rigid materialwas performed with the dielectric armor carrying 100% of the applied3000 Newton crush load with a deflection of 3 millimeters or less and100% of the bending load in order to provide an acceptable performancefor the design window.

FIGS. 9E and 9F graphically show the curves plotting the band thicknessT1 vs. a ratio (i.e., (2L2)/P) of groove length 2L2 to pitch P for thegiven total groove depths (d_(O)+d_(i)) at a given minimum strain levelfor the second rigid material. Specifically, the graph of FIG. 9Eillustrates the design window with a minimum strain of 80% and the graphof FIG. 9F depicts the design window with a minimum strain of 110%.

Thus, as shown by the tables and graphs example embodiments of the armorprofile can have dimensions within ranges based on the materials forproviding the desired crush and bending characteristics. For instance,the dielectric armor may have inner layer formed from a first rigidmaterial with minimum strain of 80% and an optional outer layer formedfrom a non-rigid material, where the band thickness T1 is between about1 millimeters and about 5 millimeters and web thickness T2 is betweenabout 0.1T1 and about T1 for the inner layer. The non-rigid materialdoes not significantly contribute to the crush and bendingcharacteristics, but can influence impact resistance and the like. Byway of example, outer layer has a suitable thickness in the range ofabout 0.5 millimeters to about 2.0 millimeters, such as about 1millimeter. Additionally, suitable armored fiber optic assemblies canhave designs outside of the modeled design windows using the samematerials because the fiber optic assembly can carry a portion of thecrush and/or bending load.

For instance, one example of an armored fiber optic assembly designsimilar to FIG. 2A where the fiber optic assembly contributes tocarrying the load uses a 24-fiber MIC cable available from Corning CableSystems of Hickory, North Carolina as the fiber optic assembly. The24-fiber MIC cable includes a cable jacket that supports the dielectricarmor during crush and bending because the free space is relativelysmall, such as about 0.5±0.2 millimeters. The dielectric armor is formedfrom an inner layer of 8015 rigid material and has a band thickness ofabout 1.5 millimeters, a web thickness of about 1 millimeter, and apitch of about 10 with a non-rigid outer layer formed from 910A-18available from Teknor Apex, which is plenum-rated. This 24-fiberembodiment advantageously meets the desired mechanical characteristicssuch as crush and bending while also being riser-rated. Other similarembodiments can meet the mechanical characteristics and have aplenum-rating. Another suitable example where the fiber optic assemblycontributes to the load carrying uses a 6-fiber MIC cable available fromCorning Cable Systems. In this embodiment, the dielectric armor is againformed from an inner layer of 8015 rigid material and has a bandthickness of about 1.3 millimeters, a web thickness of about 0.8millimeter, and a pitch of about 10 with a non-rigid outer layer formedfrom 910A-18 and is similar to the design of FIG. 2A. This 6-fiberembodiment advantageously meets the desired mechanical characteristicssuch as crush and bending while also being plenum-rated.

Other variations of armored fiber optic assemblies are also possiblethat may have other shapes for the dielectric armor. For instance, FIG.10A is a perspective view of an armored fiber optic assembly 220 thatincludes a dielectric armor 70′ having an inner layer 72 that is a rigidmaterial and an outer layer 74 that is a non-rigid material. As with theother embodiments, dielectric armor 70′ includes the armored profile andis disposed about fiber optic assembly 30 configured as a fiber opticcable. As stated above, one or both of inner layer 72 and/or outer layer74 includes web 102 and band 110. In this embodiment, the armoredprofile has web 102 and band 110 that have a fixed longitudinalorientation instead of having a spiral configuration along the length ofthe dielectric armor. In other words, the web 102 and band 110 do nottravel longitudinally along the fiber optic assembly (i.e., the lead is0).

FIG. 10B illustrates armored fiber optic assembly 320 having adielectric armor 70″ with an inner layer 72 formed from a strip 200 thatis wound or extruded around fiber optic assembly 30 in a spiral manner.In other words, strip 200 which forms inner layer 72 does not have acontinuous annular cross-section, but has a space between successivewraps of the same. As shown, strip 200 has a rectangular cross-section,but it may have rounded edges for inhibiting “zippering” of outer layer74. In other embodiments, inner layer 72 is corrugated for providingflexibility for wrapping around the fiber optic assembly 30, or isinterlocked for increased mechanical strength.

As shown, outer layer 74 conforms to inner layer 72 formed by strip 200and generally takes on a corresponding helical shape of the armorprofile. However, the shape of outer layer 74 can vary from that formedby strip 200. In an example embodiment, inner layer 70″ is wound aroundfiber optic assembly 30 using spinning, wrapping, and/or strandingmethods. The winding methods may include spinning fiber optic assembly30. Additionally, strip 200 may be pre-heated to soften the same beforebeing wound around or otherwise applied to fiber optic assembly 30 inorder to reduce the rigidity of the inner layer. It is also possible toextrude strip 200 and then wrapping the same or creating the gap thruthe wall of the inner layer. Additionally, other types of materials arepossible for portions of the dielectric armor. By way of example, innerlayer 72 may be an ultraviolet (UV)-light curable material (i.e., UVcurable material) that is helically wrapped about fiber optic assembly30, and then cured using a suitable dose of radiation. This process mayinclude applying or adding a resin to strip 200.

Finite element modeling was also performed on the embodiment of FIG. 10Bto determine designs that met the desired crush criteria as discussedabove where the strip 200 carries about 82% of the crush loading (about2468 Newtons of the 3000 Newtons). Bending was not considered sincestrip 200 has a gap G so there is no band-web separation issue like theembodiments having an inner layer with the continuous annularcross-section. Again, other embodiments can have the fiber opticassembly carry a fraction of the loading so that other variations havingthe desired performance are possible.

Table D below lists example dimensions for the strip 200 used as innerlayer 72 at different pitches about the fiber optic assembly whilemeeting the desired crush criteria. FIG. 10C shows the dimensions forstrip 200 as listed in Table D. Specifically, Table D lists differentpitches (P) for the strip 200 formed from the first rigid material (SRP2009) with an inner diameter ID of about 6.8 millimeters, a thickness ofabout 2.2 millimeters (thereby yielding an outer diameter of about 11.2millimeters), and a normal width W as listed. Additionally, Table Dlists gap GAP, an actual band width BW (i.e., the deformed width of thestrip), and a material ratio per length of the fiber optic assembly(i.e., the band width divided by the pitch). As depicted in Table D, arange of pitches P and normal widths W are possible for meeting thedesired crush loading for the embodiment of FIG. 10B. Moreover, if fiberoptic assembly carries a fraction of the loading the possible ranges forthe dimensions are larger. By way of example, the embodiments of FIG.10B can have a pitch P between about 5 millimeters and about 30millimeters and a thickness between about 1 millimeter and about 5millimeters. As given in Table D, the material ratio represents thepercentage of material usage of the strip (i.e., the smaller thematerial ratio the less material is needed per meter). For instance, thedesign having a pitch P of 26 has the most efficient use of material tomeet the desired criteria since only 47.1% of the longitudinal length ofthe assembly has the strip therearound.

TABLE D Example Dimensions for the strip of FIG. 10B Pitch (P) Width (W)Gap Band Width (BW) mm Mm mm mm Material Ratio 32 10.7 15.843 16.15750.5% 26 9.01 13.766 12.766 47.1% 20 7.71 10.560 9.440 47.2% 14 6.037.267 6.733 48.1%

Other embodiments may look similar to FIG. 10B using the strip, but havea different construction. For instance, FIG. 10D depicts armored fiberoptic assembly 420 having a dielectric armor 70′″ that looks similar toFIG. 10B, but the inner layer 72 is extruded about fiber optic assembly30, and outer layer 74 is then extruded around the inner layer 72. Inthis embodiment, both the inner layer 72 and the outer layer 74 have acontinuous annular cross-section. Specifically, inner layer 72 has auniform cross-section (i.e., a smooth tube) and the armor profile isdisposed in the outer layer 74. More specifically, outer layer 74 has avery thin web thickness such as about 0.5 millimeters or less, but othervalues are possible. Embodiments having a smooth tube for inner layer 72may have a relatively low minimum strain level such as a minimum strainof about 10% or more. For instance, one smooth tube inner layer has as aminimum strain of about 12% at a bend radius R_(B) of about 8R_(T)(i.e., 4 diameter of the armored fiber optic assembly).

One method of forming the dielectric armor includes using one or moreextrusion-based methods for forming the armor profile. For instance,FIG. 11 depicts a schematic side view of an extrusion system 300 thatincludes an extruder 302 that defines an interior 301, having a barrel303 and a screw 310 therein that is attached to a crosshead assembly(“crosshead”) 304. X-Y-Z Cartesian coordinates are shown for the sake ofreference, and the view in FIG. 11 is in the X-Y plane. Extruder 302includes screw 310 that is mechanically connected to and driven by amotor assembly 320. Motor assembly 320 includes a motor 322 and a drivesystem 324 that connects the motor to screw 310. A material hopper 330provides extrusion material 332—here, the dielectric material thatultimately makes up dielectric armor 70—to extruder 302. An explanatoryextrusion system that is suitable for being adapted for use as extrusionsystem 300 is disclosed in U.S. Pat. No. 4,181,647.

FIG. 12 is a close-up, partial cross-sectional schematic view of anexplanatory crosshead 304 as viewed in the Y-Z plane. Crosshead 304includes a tip 348 that defines a central channel 350 having an outputend 352 and in which is arranged a profile tube 360 having an outersurface 361, an inner surface 362 that defines a tube interior 363, aproximal (output) end 364, and a distal end 365. A profiling feature 370is located on outer surface 361 at output end 352. In an exampleembodiment, profiling feature 370 is a nub or a bump. Profile tubeinterior 363 is sized to accommodate fiber optic assembly 30 axially.Profile tube distal end 365 is centrally engaged by a gear 374 that, inturn, is driven by a motor (not shown) in a manner such that profiletube 360 rotates within channel 350.

Crosshead 304 further includes a die 378 arranged relative to tip 348 toform a cone-like material channel 380 that generally surrounds centralchannel 350 and that has an output end 382 in the same plane as channeloutput end 352. Material channel 380 is connected to extruder interior301 so as to receive extrusion material 332 therefrom and through whichflows the extrusion material during the extrusion process to form one ormore layers of the dielectric armor. In the example embodiment ofcrosshead 304 of FIG. 12, profile tube output end 365 extends beyondchannel output end 352 such that profiling feature 370 thereon residesadjacent material channel output end 382. In an example embodiment,profile tube 360 and tip 348 are integrated to form a unitary tool.

In forming armored fiber optic assemblies 20, extrusion material (notshown) flows through material channel 380 and out of material channeloutput end 382. At the same time, fiber optic assembly 30 is fed throughprofile tube interior 363 and out of profile tube output end 364 (andthus through tip 348 and die 378). In the meantime, profile tube 360 isrotated via gear 374 so that profiling feature 370 redirects (i.e.,shapes) the flow of the extrusion material as it flows about fiber opticassembly 30. As fiber optic assembly 30 moves through profile tubeoutput end 364, the circular motion of profiling feature 370 diverts theflow of extrusion material. When motion of the profiling feature 370 iscombined with the linear motion of fiber optic assembly 30 the flow ofthe extrusion material forms an armored profile. The speed at whichprofile tube 360 rotates relative to the motion of fiber optic assembly30 (which may also be rotating) dictates the pitch of the same. Forinstance, all things being equal higher rotational speeds for theprofiling feature 370 results in a shorter pitch. The size and shapecharacteristics of profiling feature 370 dictate, at least in part, theparticular armor profile imparted to an outer surface 80 of thedielectric armor. Though the extrusion flow is primarily diverted on theinterior of the armor, the drawdown of the material moves the groovepartially or completely to the outer surface of the armor. Of course,this type of extrusion set-up may be used on any desired layer of thedielectric armor.

Additionally, there are other suitable methods for forming the armorprofile. By way of example, FIG. 13 schematically illustrates thedielectric armor 70 initially being extruded as a smooth-surfaced tube(i.e., having a smooth outer surface as shown on the right-side).Thereafter, the armor profile of the outer surface 80 is then formed inthe smooth-surfaced tube, prior to hardening, by the application (e.g.,pressing) of a deforming member 402 (e.g., a nub or a finger) into thelayer so as to shape outer surface 80 in a manner similar to that usedin a lathe. In this example, the deforming member 402 may simply divertmaterial from the web to the band, or it may remove material entirelyfrom the dielectric armor 70. In one example embodiment, deformingmember 402 is stationary and cable 20 is rotated, while in anotherexample embodiment, deforming member 402 rotates around the dielectricarmor 70 as it passes. In still another example embodiment, both thedielectric armor 70 and deforming member 402 rotate. Deforming member402 may also be integrated into the extrusion tooling (die).

FIG. 14 is a close-up, schematic cross-sectional view of anotherexplanatory embodiment of crosshead 304′ similar to that shown in FIG.12, wherein tip 348 and die 378 are configured so that central channel350 is combined with the material channel that flows extrusion material332 therethru. A portion of profile tube 360 resides in an interiorregion 349 of tip 348, while the proximal end portion of the profiletube resides within channel 350 so that profiling feature 370 resideswithin central channel 350 adjacent to channel output end 352. Thisgeometry allows for controlling the flow of extrusion material 332 whileconfining the material within die 378.

In another explanatory embodiment similar to that shown in FIG. 13 andas illustrated in FIGS. 15 and 16, the dielectric armor is initiallyextruded as a smooth-surfaced tube (i.e., having a smooth outer surfaceon the right-side) using dielectric material 332. The armor profile ofouter surface 80 is then formed prior to hardening, by the application(e.g., pressing) of deforming member 402 (e.g., a set of gears) havingone or more features 404 that press into the dielectric armor in orderto shape outer surface 80. FIG. 16 shows a perspective view of anexemplary embodiment of a roller-type deforming member 402 having anouter edge 403 in which features 404 are formed. In this embodiment,deforming member 402 of FIG. 15 may be formed in sets of two, three,four, or more for forming the desired armor profile. Roller-typedeforming member 404 rolls over the outer surface 80 of the dielectricarmor before it hardens, thereby impressing features 404 and forming thearmor profile.

Additionally, deforming member 402 may press extrusion material 332against fiber optic assembly 30 to eliminate free space 90. Deformingmember 402 may also press against dielectric armor 70 in a manner thatmaintains the desired amount of free space 90. FIG. 17 is a front viewthat illustrates the use of two roller-type deforming member to impressthe desired armor profile into the dielectric armor. Of course, theroller-type deforming member can have any desired pattern for creatingthe desired armored profile.

Bend-Insensitive Multimode Fibers

As mentioned above, in an example embodiment, the at least one opticalfiber 40 is a BR-MM fiber. FIG. 18 is a side view of an example BR-MMfiber 40, which has a central axis or “centerline” A_(C). FIG. 19 is anexample cross-sectional view of BR-MM fiber 40 of FIG. 18 as viewedalong the direction 19-19. FIG. 20 shows a schematic representation ofthe refractive index profile BR-MM fiber 40. BR-MM fiber 40 has a glasscore 41 and a glass cladding 42, the cladding comprising an innerannular portion 43, a depressed-index annular portion 44, and an outerannular portion 45. Core 41 has outer radius R1 and maximum refractiveindex delta Δ1MAX. The inner annular portion 43 has width W2 and outerradius R2. Depressed-index annular portion 44 has minimum refractiveindex delta percent Δ3MIN, width W3 and outer radius R3. Thedepressed-index annular portion 44 is shown offset, or spaced away, fromthe core 41 by the inner annular portion 43. Annular portion 44surrounds and contacts the inner annular portion 43. The outer annularportion 45 surrounds and contacts the annular portion 44. The clad layer42 is surrounded by at least one coating 46, which may in someembodiments comprise a low modulus primary coating and a high modulussecondary coating. An example BR-MM fiber 40 is the CLEARCURVE®multimode fiber, available from Corning, Inc., Corning, N.Y.

An example inner annular portion 43 has a refractive index profile Δ2(r)with a maximum relative refractive index Δ2MAX, and a minimum relativerefractive index Δ2MIN, where in some embodiments Δ2MAX=Δ2MIN. Anexample depressed-index annular portion 44 has a refractive indexprofile Δ3(r) with a minimum relative refractive index Δ3MIN. An exampleouter annular portion 45 has a refractive index profile Δ4(r) with amaximum relative refractive index Δ4MAX, and a minimum relativerefractive index Δ4MIN, where in some embodiments Δ4MAX=Δ4MIN.Preferably, Δ1 MAX>Δ2MAX>Δ3MIN. In some embodiments, the inner annularportion 43 has a substantially constant refractive index profile, asshown in FIG. 20 with a constant Δ2(r); in some of these embodiments,Δ2(r)=0%. In some embodiments, the outer annular portion 45 has asubstantially constant refractive index profile, as shown in FIG. 20with a constant Δ4(r); in some of these embodiments, Δ4(r)=0%. The core41 has an entirely positive refractive index profile, where Δ1(r)>0%.Radius R1 is defined as the radius at which the refractive index deltaof the core first reaches value of 0.05%, going radially outwardly fromthe centerline A_(C). Preferably, the core 41 contains substantially nofluorine, and more preferably the core 41 contains no fluorine. In someembodiments, the inner annular portion 42 preferably has a relativerefractive index profile Δ2(r) having a maximum absolute magnitude lessthan 0.05%, and Δ2MAX<0.05% and Δ2MIN>−0.05%, and the depressed-indexannular portion 44 begins where the relative refractive index of thecladding first reaches a value of less than −0.05%, going radiallyoutwardly from the centerline. In some embodiments, the outer annularportion 45 has a relative refractive index profile Δ4(r) having amaximum absolute magnitude less than 0.05%, and Δ4MAX<0.05% andΔ4MIN>−0.05%, and the depressed-index annular portion 44 ends where therelative refractive index of the cladding first reaches a value ofgreater than −0.05%, going radially outwardly from the radius whereΔ3MIN is found.

BR-MM fiber 40 may comprise a graded-index core 41 and a cladding 42surrounding and directly adjacent to the core region, with the claddingregion comprising a depressed-index annular portion 44 comprising adepressed relative refractive index relative to another portion of thecladding. The depressed-index annular portion 44 of the cladding ispreferably spaced apart from the core. Preferably, the refractive indexprofile of the core 41 has a parabolic or substantially curved shape.The depressed-index annular portion 44 may, for example, comprise a)glass comprising a plurality of voids, or b) glass doped with one ormore downdopants such as fluorine, boron, individually or mixturesthereof. The depressed-index annular portion may have a refractive indexdelta less than about −0.2% and a width of at least about 1 micron, withthe depressed-index annular portion being spaced from said core by atleast about 0.5 microns.

In some embodiments, BR-MM fiber 40 comprises a cladding with voids, thevoids in some preferred embodiments are non-periodically located withinthe depressed-index annular portion. “Non-periodically located” meansthat if takes a cross section (such as a cross section perpendicular tothe longitudinal axis) of the optical fiber, the non-periodicallydisposed voids are randomly or non-periodically distributed across aportion of the fiber (e.g. within the depressed-index annular region).Similar cross sections taken at different points along the length of thefiber will reveal different randomly distributed cross-sectional holepatterns, i.e., various cross sections will have different holepatterns, wherein the distributions of voids and sizes of voids do notexactly match for each such cross section. That is, the voids arenon-periodic, i.e., they are not periodically disposed within the fiberstructure. These voids are stretched (elongated) along the length (i.e.generally parallel to the longitudinal axis) of the optical fiber, butdo not extend the entire length of the entire fiber for typical lengthsof transmission fiber. It is believed that the voids extend along thelength of the fiber a distance less than about 20 meters, morepreferably less than about 10 meters, even more preferably less thanabout 5 meters, and in some embodiments less than 1 meter.

BR-MM fiber 40 exhibits very low bend induced attenuation, in particularvery low macrobending induced attenuation. In some embodiments, highbandwidth is provided by low maximum relative refractive index in thecore, and low bend losses are also provided. Consequently, BR-MM fiber40 fiber may comprise a graded index glass core; and an inner claddingsurrounding and in contact with the core, and a second claddingcomprising a depressed-index annular portion surrounding the innercladding, said depressed-index annular portion having a refractive indexdelta less than about −0.2% and a width of at least 1 micron, whereinthe width of said inner cladding is at least about 0.5 microns and thefiber further exhibits a 1 turn, 10 mm diameter mandrel wrap attenuationincrease of less than or equal to about 0.4 dB/turn at 850 nm, anumerical aperture (NA) of greater than 0.14, more preferably greaterthan 0.17, even more preferably greater than 0.18, and most preferablygreater than 0.185, and an overfilled bandwidth greater than 1.5 GHz-kmat 850 nm. By way of example, the numerical aperture for BR-MM fiber 40is between about 0.185 and about 0.215.

In an example embodiment, core 41 has a 50 micron diameter while inanother example embodiment has a 62.5 micron core diameter. Such BR-MMfibers 40 can be made to provide (a) an overfilled (OFL) bandwidth ofgreater than 1.5 GHz-km, more preferably greater than 2.0 GHz-km, evenmore preferably greater than 3.0 GHz-km, and most preferably greaterthan 4.0 GHz-km at an 850 nm wavelength. By way of example, these highbandwidths can be achieved while still maintaining a 1 turn, 10 mmdiameter mandrel wrap attenuation increase at an 850 nm wavelength ofless than 0.5 dB, more preferably less than 0.3 dB, even more preferablyless than 0.2 dB, and most preferably less than 0.15 dB. These highbandwidths can also be achieved while also maintaining a 1 turn, 20 mmdiameter mandrel wrap attenuation increase at an 850 nm wavelength ofless than 0.2 dB, more preferably less than 0.1 dB, and most preferablyless than 0.05 dB, and a 1 turn, 15 mm diameter mandrel wrap attenuationincrease at an 850 nm wavelength, of less than 0.2 dB, preferably lessthan 0.1 dB, and more preferably less than 0.05 dB. Such fibers arefurther capable of providing a numerical aperture (NA) greater than0.17, more preferably greater than 0.18, and most preferably greaterthan 0.185. Such fibers are further simultaneously capable of exhibitingan OFL bandwidth at 1300 nm which is greater than about 500 MHz-km, morepreferably greater than about 600 MHz-km, even more preferably greaterthan about 700 MHz-km. Such fibers are further simultaneously capable ofexhibiting minimum calculated effective modal bandwidth (Min EMBc)bandwidth of greater than about 1.5 MHz-km, more preferably greater thanabout 1.8 MHz-km and most preferably greater than about 2.0 MHz-km at850 nm.

Preferably, BR-MM fiber 40 exhibits a spectral attenuation of less than3 dB/km at 850 nm, preferably less than 2.5 dB/km at 850 nm, even morepreferably less than 2.4 dB/km at 850 nm and still more preferably lessthan 2.3 dB/km at 850 nm. Preferably, BR-MM fiber 40 exhibits a spectralattenuation of less than 1.0 dB/km at 1300 nm, preferably less than 0.8dB/km at 1300 nm, even more preferably less than 0.6 dB/km at 1300 nm.

In some embodiments, the core 41 extends radially outwardly from thecenterline A_(C) to a radius R1, wherein 10≦R1≦40 microns, morepreferably 20≦R1≦40 microns. In some embodiments, 22≦R1≦34 microns. Insome preferred embodiments, the outer radius of the core 41 is betweenabout 22 to 28 microns. In some other preferred embodiments, the outerradius of the core is between about 28 to 34 microns.

In some embodiments, the core 41 has a maximum relative refractiveindex, less than or equal to 1.2% and greater than 0.5%, more preferablygreater than 0.8%. In other embodiments, the core has a maximum relativerefractive index, less than or equal to 1.1% and greater than 0.9%.

In some embodiments, BR-MM fiber 40 exhibits a 1 turn, 10 mm diametermandrel attenuation increase of no more than 1.0 dB, preferably no morethan 0.6 dB, more preferably no more than 0.4 dB, even more preferablyno more than 0.2 dB, and still more preferably no more than 0.1 dB, atall wavelengths between 800 and 1400 nm. Example BR-MM fibers 40 arealso disclosed in U.S. patent application Ser. Nos. 12/250,987 filed onOct. 14, 2008, and 12/333,833 filed on Dec. 12, 2008, the disclosures ofwhich are incorporated herein by reference.

FIG. 21 is a plot of the change in attenuation (“Δ attenuation”) in dBversus bend radius in mm for standard 50 micron MM and 50 micron BR-MMfiber 40 at wavelengths of 850 nm and 1,300 nm. The bend radius wasestablished using two wraps around mandrels having radii of 4.2 mm, 5.4mm and 10.4 mm. A bend test around a 120 mm diameter mandrel as used tomodel projected attenuation for both the standard multimode fiber andBR-MM fiber 40. The modeling indicates that the BR-MM fiber 40 providesabout a 4× attenuation benefit at 850 nm and about a 2× benefit at 1,300nm.

Fiber optic assemblies according to the present embodiments may haveexceptionally low delta attenuations when subjected to bending. Forexample, a fiber optic assembly 20 as generally shown in FIG. 3Asubjected to a mandrel wrap about a 120 millimeter mandrel may exhibitvery low delta attenuation. In a fiber optic assembly having six fibers,simulated test data indicate the multimode fibers in the assembly 20will exhibit a delta attenuation of less than 0.2 decibels at awavelength of 850 nanometers, and delta attenuation of less than 0.4decibels at 1300 nanometers, when wrapped around the mandrel six times.Selected fibers in the assembly 20 may experience a delta attenuation ofless than 0.15 decibels at 850 nanometers, and less than 0.35 decibelsat 1300 nanometers, when wrapped around the mandrel six times.

Example

A fiber optic assembly 20 as shown in FIG. 3A has an armor 70 outsidediameter of 9.1 mm, tube 32 diameter of 4.4 mm, includes fourCLEARCURVE® multimode fibers 40 and two 50 micron single mode fibers.When wrapped around a 120 millimeter diameter mandrel six times, thefour multimode fibers respectively exhibit delta attenuations of about0.14 dB, 0.05 dB, 0.07 dB, and 0.10 dB at 850 nanometers, when wrappedaround the mandrel six times. At 1300 nanometers, the fibersrespectively exhibit delta attenuations of about 0.32 dB, 0.13 dB, 0.17dB, and 0.21 dB, when wrapped around the mandrel six times.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit and scope of the invention. Thus, itis intended that the present invention cover the modifications andvariations of this invention, provided they come within the scope of theappended claims and their equivalents.

We claim:
 1. An armored fiber optic assembly, comprising: a fiber opticassembly having at least one optical fiber; and a dielectric armorsurrounding the fiber optic assembly, the dielectric armor comprising atleast one layer formed from a rigid material and having an armorprofile, wherein the armor profile has a band thickness T1 and a webthickness T2, the band thickness T1 is between about 0.5 millimeters andabout five millimeters, the web thickness T2 is in the range of0.1T1≦T2≦T1, and when the armored fiber optic assembly is wrapped arounda mandrel having a diameter of 120 millimeters six times, the at leastone optical fiber exhibits at least one of: a delta attenuation of lessthan 0.2 decibels at a wavelength of 850 nanometers, and a deltaattenuation of less than 0.4 decibels at a wavelength of 1300nanometers.
 2. The armored fiber optic assembly of claim 1, wherein theat least one layer has a continuous annular cross-section.
 3. Thearmored fiber optic assembly of claim 2, wherein the armor profile has apitch P between about 5 millimeters and about 30 millimeters.
 4. Thearmored fiber optic assembly of claim 2, wherein the armor profile has agroove length that is between about 20 percent and 80 percent of a pitchP.
 5. The armored fiber optic assembly of claim 2, wherein the armoredfiber optic assembly has a free space of about 2 millimeters or lessbetween an outer surface of the fiber optic assembly and an innersurface of the dielectric armor.
 6. The armored fiber optic assembly ofclaim 2, wherein the at least one layer comprises PVC.
 7. The armoredfiber optic assembly of claim 1, wherein the armored fiber opticassembly has a free space of about 2 millimeters or less between anouter surface of the fiber optic assembly and an inner surface of thedielectric armor.
 8. The armored fiber optic assembly of claim 1,wherein when the armored fiber optic assembly is wrapped around amandrel having a diameter of 120 millimeters six times, the at least oneoptical fiber exhibits a delta attenuation of less than 0.35 decibels ata wavelength of 1300 nanometers.
 9. The armored fiber optic assembly ofclaim 1, wherein the armor profile has a pitch P between about 5millimeters and about 30 millimeters.
 10. The armored fiber opticassembly of claim 1, wherein the armor profile has a groove length thatis between about 20 percent and 80 percent of a pitch P.
 11. The armoredfiber optic assembly of claim 1, wherein the armored fiber opticassembly has a free space of about 2 millimeters or less between anouter surface of the fiber optic assembly and an inner surface of thedielectric armor.
 12. The armored fiber optic assembly of claim 1,wherein the at least one layer comprises PVC.
 13. An armored fiber opticassembly, comprising: a fiber optic assembly having at least one opticalfiber and a dielectric armor with an armor profile, the dielectric armorcomprising at least one layer formed from a rigid material, wherein thearmor profile has a band thickness T1 and a web thickness T2, the bandthickness T1 is between about 0.5 millimeters and about 5 millimeters,and when the armored fiber optic assembly is wrapped around a mandrelhaving a diameter of 120 millimeters six times, the at least one opticalfiber exhibits a delta attenuation of less than 0.4 decibels at awavelength of 1300 nanometers.
 14. The armored fiber optic assembly ofclaim 13, wherein the inner layer has a continuous annularcross-section.
 15. The armored fiber optic assembly of claim 13, whereinthe armor profile has a pitch P between about 5 millimeters and about 30millimeters, and a groove length that is between about 20 percent and 80percent of the pitch P.
 16. The armored fiber optic assembly of claim13, wherein the armored fiber optic assembly has a free space of about 2millimeters or less between an outer surface of the fiber optic assemblyand an inner surface of the dielectric armor.
 17. The armored fiberoptic assembly of claim 13, wherein when the armored fiber opticassembly is wrapped around a mandrel having a diameter of 120millimeters six times, the at least one optical fiber exhibits a deltaattenuation of less than 0.2 decibels at a wavelength of 850 nanometers.18. An armored fiber optic assembly, comprising: a fiber optic assemblyhaving at least one optical fiber; a dielectric armor formed about thefiber optic assembly, the dielectric armor having an armor profile, thearmored fiber optic assembly has a diametral deflection of 3.3millimeters or less during a crush resistance test, wherein the crushresistance test applies a load of 300 Newtons/centimeter over a 10centimeter length of the armored fiber optic assembly for a period often minutes, wherein when the armored fiber optic assembly is wrappedaround a mandrel having a diameter of 120 millimeters six times, the atleast one optical fiber exhibits a delta attenuation of less than 0.2decibels at a wavelength of 850 nanometers.
 19. The armored fiber opticassembly of claim 18, wherein when the armored fiber optic assembly iswrapped around a mandrel having a diameter of 120 millimeters six times,the at least one optical fiber exhibits a delta attenuation of less than0.4 decibels at a wavelength of 1300 nanometers.
 20. The armored fiberoptic assembly of claim 18, wherein when the armored fiber opticassembly is wrapped around a mandrel having a diameter of 120millimeters six times, the at least one optical fiber exhibits a deltaattenuation of less than 0.35 decibels at a wavelength of 1300nanometers.